Driving circuit for a fluorescent display apparatus having fewer leads

ABSTRACT

A fluorescent display apparatus having a plurality of anodes linearly arranged and divided into consecutive several groups each containing the same number of anodes. Each of the anodes disposed in corresponding positions of the respective anode groups is electrically connected in parallel, and a control grid is provided in each of the anode groups in an opposed relation. A particular anode representing the value of an input signal is illuminated by energizing one of the anodes in the respective anode groups and one of the control grids.

This is a division, of application Ser. No. 098,690, filed Nov. 29, 1979U.S. Pat. No. 4,325,064.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a display apparatus, and moreparticularly to a fluorescent display apparatus suitable for indicatinga frequency in a wireless telegraphic apparatus, a numerical value inmeasuring instruments or the like.

2. Description of the Prior Arts

In the conventional radio receiver or the like, the frequency receivedby the radio receiver is indicated by a moving pointer which movesmechanically using a driving mechanism along a dial or scale on whichcalibrations of frequency are shown.

Recently, with the development and practical use of various displayelements, an indicating apparatus, such as, for example, a frequencyindicating device explained above, in the form of an electronic devicehas come into actual use. The electronic indicating device remarkablyimproves such various deficiencies in the mechanical indicatingapparatus such as not being strong enough to withstand external shock,being fragile, requiring more mounting space, and being difficult toread the calibrations at night or in a dark place.

The electronic indicating apparatus includes, as shown in FIG. 1,display elements 1 which may be made of light emitting diodes, anodeshaving deposited phosphor layers thereon to emit light upon impingementof electrons, or discharge cells which are filled with ionizable gas andemit light by gas discharge. The display elements 1 are linearly orcurvedly arranged, and the calibrations 2 which may be made of displayelements similar to the elements 1 are provided adjacent to the displayelements 1. The display is effected by energizing a predetermineddisplay element among the linearly or curvedly arranged display elementsin accordance with an input signal to be displayed.

However, in the conventional display apparatus of this type, it isnecessary to extend a number of lead wires corresponding to the numberof the display elements 1 out of an envelope of the display apparatus,because the display is effected by selectively energizing one of thedisplay elements related to the input signal. Thus, there must beprovided an increased number of lead wires and driving sections forenergizing each of the display elements separately, which makes itdifficult to effect minute display in the display device and increasesthe manufacturing costs.

In other words, it is difficult to increase the number of the displayelements 1 arranged on the display apparatus in order to enhance theresolution of the display, and also it is difficult to make the displayrange wide. A static driving system and a dynamic driving system forsuch a display are known. The static driving system drives the displayapparatus by applying a drive signal individually to each of the displayelements 1 as explained above. The dynamic driving system effects thedisplay by applying a display signal to the display elements 1 which aredivided into consecutive groups with connections between thecorresponding positions of each of the groups and by scanning each groupof the anodes with pulse signals.

In the dynamic driving system, it is possible to significantly decreasethe number of lead wires which come out of the envelope of the displaydevice. However, this system is not acceptable as a driving system ofcommunication appliances or measuring instruments, because the scanningpulses for each group of the anodes create noise in the adjacentcommunication appliances or measuring instruments and cause themalfunction of these appliances.

BRIEF SUMMARY OF THE INVENTION

Therefore, the present invention is intended to eliminate theabove-mentioned disadvantages of the prior art.

It is an object of the present invention to provide a fluorescentdisplay apparatus which is capable of being driven at relatively lowvoltage and is low in power consumption, and yet capable of obtaining agreen luminous color which is extremely easy to observe, or capable ofobtaining an optional luminous color.

It is another object of the present invention to provide a fluorescentdisplay apparatus which includes fewer lead wires extending outside theenvelope of the display device similar to a dynamic driving system andis capable of illuminating a particular display element which is relatedto an input signal without causing any hazardous noise to adjacentelectric appliances.

According to the present invention, the foregoing and other objects areattained by providing a fluorescent display apparatus in which aplurality of anodes each coated with a phosphor layer on the uppersurfaced thereof are linearly arranged and divided into severalconsecutive groups each containing the same number of anodes. Each ofthe anodes disposed in corresponding positions of the respective anodegroups is electrically connected in parallel, and a control electrode ismounted above each of the anode groups. The fluorescent displayapparatus further includes a first decoder for decoding the leastsignificant digit of an input signal to be displayed and for applyingthe same to each of the corresponding anodes in the respective anodegroups, and a second decoder for decoding a more significant digit ofthe input signal and for applying the same to any one of the controlelectrodes so that the particular anode representing the value of theinput signal which is selected by the first and second decoders may beilluminated.

BRIEF DESCRIPTION OF DRAWINGS

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the figuresthereof and wherein:

FIG. 1 is a schematic diagram illustrating an arrangement of displayelements in a fluorescent display apparatus according to the presentinvention;

FIG. 2 is a block schematic diagram showing an embodiment of afluorescent display apparatus according to the present invention;

FIG. 3 is a block schematic diagram showing another embodiment of afluorescent display apparatus according to the present invention; and

FIG. 4 is a block schematic diagram illustrating an application of afluorescent display apparatus according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A fluorescent display device according to the present invention will behereinafter described with reference to the accompanying drawings.

FIG. 2 is a block schematic diagram showing an embodiment of afluorescent display apparatus according to the present invention. Inthis embodiment, one hundred display elements are linearly arranged sothat a predetermined display element corresponding to one of thenumerals, "0" to "99" may be illuminated. In the fluorescent displayapparatus shown in FIG. 2, an input signal is applied to the apparatusof a BCD signal.

In FIG. 2, the fluorescent display apparatus generally indicated by thereference numeral 10 includes an insulating substrate (not shown) onwhich one hundred anodes 11 having fluorescent layers deposited thereonare linearly arranged. Reference numeral 13 designates grids which aremounted opposite to a certain number of the anodes 11 (ten anodes in theembodiment shown in FIG. 2) and which are electrically isolated from oneanother. In addition, there is provided a filamentous cathode (notshown) above the grids 13 which emits thermions when energized andheated.

Reference numeral 12 indicates a graduated scale as a reference for thenumeral of the illuminated anode 11. Reference numeral 14 designatesinner leads for connecting each of the electrodes. The inner leads 14connect each of the anodes disposed in corresponding portions of therespective grids 13 together, which are in turn connected to outer leads15a for leading out of the display apparatus. Each of the grids 13 isled out of the display apparatus by the respective outer leads 15b.

These electrodes and inner leads are hermetically sealed within a vacuumenvelope having a transparent viewing window so as to form thefluorescent display apparatus 10.

The fluorescent display apparatus 10 explained herein above is of astructure to which the conventional dynamic driving system is applied.According to this driving system, the fluorescent display apparatus maybe provided with fewer external terminals 15a and 15b equal to the sumof the number of the grids 13, the number of the anodes 11 of each grid13, and the number of the leads for supplying electric power to thecathode.

Reference numeral 16 is a signal converting section for converting aninput signal given by the BCD signal into a driving signal for thefluorescent display apparatus 10. In this embodiment, the signalconverting section 10 includes a first and second decoders 16a and 16bfor converting a more significant digit and the least significant digitof the input signal into a decimal numeral, respectively.

According to the above construction, when the input signal to bedisplayed is given to the signal converting section 16, the numericalvalue of the least significant digit of the input signal is decoded bythe decoder 16a, and the driving signal is supplied to any one ofterminals, "0" to "9" which is connected to the anodes 11 of each grid13.

In the other hand, the numerical value of the more significant digit ofthe input signal is decoded by the decoder 16b, and any one of ten grids13 is selected. Then, electrons emitted from the cathode are impingedupon only the anode 11 selected by the decoder 16a and subjected to thegrid 13 which is selected by the decoder 16b, thereby to illuminate theparticular anode 11 corresponding to the numerical value of the inputsignal.

According to the fluorescent display apparatus of the present inventionwhich uses the dynamic driving system, it is possible to eliminate anumber of the outer leads 15a and 15b, which results in an increase ofthe number of anodes 11 arranged on the substrate. As a result,resolution of the display is significantly increased, and the displayrange can be widened. In addition, the number of the driving circuitscan be decreased.

The fluorescent display device according to the present invention doesnot generate any signal which causes external appliance noises, becausethe fluorescent display apparatus 10 is driven without using a pulse.Therefore, it is extremely suitable for an indicating portion of variouscommunication appliances, measuring instruments, and the like.

Reference will now be made to a practical example in which theindicating apparatus of the present invention is used as a frequencyindicator of the medium wave radio receiver shown in FIG. 3.

In general, the medium wave radio receiver receives frequencies of535-1605 KHZ. Therefore, it is necessary to provide at least elevengrids 13 to cover all of the frequencies.

In the embodiment shown in FIG. 3, a signal converting section 16 isformed of a decoder 16a for decoding the numerical value of the leastsignificant digit of the input signal (the numerical value of tenfigures is the least significant digit in this case), two decoders 16band 16c for decoding the numerical value of the more significant digits,and an "AND" circuit 16d for selecting a predetermined grid 13 from twooutput signals generated by the decoders 16b and 16c. The "AND" circuit16d selects either a combination of "0" signal from the decoder 16c and"5" signal from the decoder 16b or a combination of "1" signal from thedecoder 16c and "0"-"5" signals from the decoder 16b and energizes thecorresponding grid 13. "6"-"9" signals from the decoder 16 are appliedto the corresponding grids 13 not through the "AND" circuit 16d.

According the embodiment shown in FIG. 3, when the input signal to bedisplayed is applied to the signal converting section 16, the numericalvalue of the least significant digit of the input signal is decoded bythe decoder 16a, and the driving signal is supplied to any one ofterminals, "0" to "0" and one of the anodes 11 of each grid 13 isselected. On the other hand, the numerical value of the more significantdigits of the input signal is decoded by the two decoders 16b and 16c,and the signals from the decoders 16b and 16c are transmitted to the"AND" circuit 16d in which any one of eleven grids 13 is selected. Then,electrons emitted from the cathode are impinged only upon the anode 11selected by the decoder 16a and subjected to the grid 13 which isselected by the "AND" circuit 16d, thereby to illuminate the particularanode 11 corresponding to the numerical value of the input signal. Inthis embodiment, the unidecimal decoder can be formed by the twodecoders 16b and 16c and the "AND" circuit 16d, because four bits binarycode decoder is used in this invention.

Referring now to an embodiment in which the indicating apparatus of thepresent invention is incorporated into a frequency tuning circuit ofradio receiver shown in FIG. 4, the frequency tuning circuit is made upof a PLL (Phase Locked Loop) frequency synthesizer comprising areference oscillator 21 using a quartz oscillator as a local oscillatingcircuit, a frequency demultiplier 22, a phase detector 23, a low passfilter 24, a variable capacity diode 25, a voltage control oscillator 26for regulating the oscillating frequency in response to a voltageapplied to the variable capacity diode 25, and a programmable counter 27for receiving a set signal. In this apparatus, the tuning of theintended frequency can be correctly indicated by introducing the setsignal of the programmable counter 27 into a signal indicating portion16 in order to decode the signal into a driving signal for thefluorescent display apparatus.

As explained above, the fluorescent display apparatus according to thepresent invention includes a plurality of anodes divided intoconsecutive groups, and each of the anodes disposed in correspondingportions of the respective groups is electrically connected in commonsimilar to the fluorescent display tube driven by the dynamic drivingsystem. Therefore, the number of the lead wires extended to the outsideof the vacuum casing can be minimized, which results in the increase ofthe number of anodes arranged on the substrate. Thus, resolution of thedisplay is significantly increased, and also the display range can bewidened. In addition, the fluorescent display apparatus according to thepresent invention can be driven with a simple circuit including fewerdriving circuits for each of the anodes. This is advantageous in view ofthe manufacturing costs furthermore, the fluorescent display apparatusaccording to the present invention does not require high frequencyscanning pulses to drive the apparatus similar to the static drivingsystem. Thus, unnecessary electric waves which induce noise in adjacentelectric appliances are not generated from the display apparatus.Accordingly, even when it is used as an indicating portion of variouscommunication appliances, audio appliances, measuring instruments, andthe like, there is no fear of generating hazardous noises.

Obviously, many modification and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A fluorescent display apparatus comprising:avacuum casing made up of a substrate and a front cover airtightly bondedtogether; a plurality of anodes each coated with a phosphor layer on theupper surfaces thereof and disposed on said substrate; said anodes beingdivided into consecutive several groups so as to include a certainnumber of anodes in each of said anode groups; each of said anodesdisposed in corresponding positions of said respective anode groupsbeing connected together in parallel; a plurality of control electrodeseach provided in an opposite relationship with respect to saidrespective anode groups; a filamentary cathode stretched above saidcontrol electrodes for emitting thermions when energized and heated; afirst decoder means for decoding the least significant digit of an inputsignal and for driving a plurality of anodes having correspondingpositions in said respective anode groups with a continuous signal; anda second decoder means for decoding at least one more significant digitof said input signal and for driving one of said control electrodes witha continuous signal, whereby one of said anodes selected by said firstand second decoders representing the value of said input signal isilluminated and said fluorescent display apparatus is substantiallynoise-free.